Airfoils and Machines Incorporating Airfoils

ABSTRACT

Various embodiments of an airfoil and machines with airfoils are disclosed. The airfoils include a thicker leading airfoil portion and a thinner trailing airfoil portion. In one embodiment, the leading airfoil portion is formed by bending a body of the airfoil back toward itself. In another embodiment, the leading airfoil portion has a solid geometry and includes two elliptic surfaces. To prevent detachment of airflow, the leading airfoil portion includes at least two arc portions or surfaces that act to direct the airflow down to the trailing airfoil portion in a manner that stabilizes vortexes that may form in the region of changing thickness.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationNo. 62/611,890, filed Dec. 29, 2017, and titled “Airfoils and MachinesIncorporating Airfoils,” the entirety of which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

The present invention relates generally to airfoils and machinesincluding airfoils.

Airfoils produce an aerodynamic force as they move through a fluid,generating lift and drag. Subsonic flight airfoils may have a shape witha rounded leading edge and a sharp trailing edge. In some airfoils, theupper and lower surfaces may have similar curvature.

Airfoils may be used in a variety of machines including turbines,propellers, fans as well as other kinds of machines.

SUMMARY OF THE INVENTION

In one aspect, an airfoil includes a leading edge and a trailing edge, asuction side and a pressure side, a base portion including a firstsurface associated with the pressure side and a second surfaceassociated with the suction side. The airfoil also includes an overhangportion that extends over some of the base portion and an ellipticportion connecting the base portion and the overhang portion adjacentthe leading edge. The overhang portion is curved toward the secondsurface of the base portion.

In another aspect, an airfoil includes a leading edge and a trailingedge, a suction side and a pressure side, a leading airfoil portionincluding the leading edge and a trailing airfoil portion including thetrailing edge. The leading airfoil portion includes a pressure sidesurface, a first elliptic surface, a suction side surface and a secondelliptic surface. The first elliptic surface connects the pressure sidesurface with the suction side surface and the second elliptic surfaceconnects the suction side surface with the suction side of the trailingairfoil portion. A thickness of the airfoil decreases from the leadingairfoil portion to the trailing airfoil portion.

In another aspect, an airfoil for use with a motor vehicle trailerincludes a base portion and an extended portion extending from the baseportion. The base portion includes a lower periphery, a first surfaceand a second surface, where the first surface extends from the lowerperiphery to the extended portion and where the second surface extendsfrom the lower periphery to the extended portion. The extended portionextends over the second surface.

Other systems, methods, features, and advantages of the invention willbe, or will become, apparent to one of ordinary skill in the art uponexamination of the following figures and detailed description. It isintended that all such additional systems, methods, features, andadvantages be included within this description and this summary, bewithin the scope of the invention, and be protected by the followingclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention. Moreover, in the figures, likereference numerals designate corresponding parts throughout thedifferent views.

FIG. 1 is a schematic isometric view of an embodiment of an airfoilalong the pressure side;

FIG. 2 is a schematic isometric view of a suction side of the airfoil ofFIG. 1;

FIG. 3 is a schematic side view of an embodiment of an airfoil;

FIG. 4 is a schematic side view of the airfoil of FIG. 3, in which thecurvature of various portions of the airfoil are indicated;

FIG. 5 is a schematic view of an embodiment of an airfoil indicatingpathlines of airflow elements;

FIG. 6 is a schematic isometric view of another embodiment of anairfoil;

FIG. 7 is a schematic side view of the airfoil of FIG. 6, in which thecurvature of various portions of the airfoil are indicated;

FIG. 8 is a schematic view of an embodiment of an airfoil indicatingpathlines of airflow elements;

FIG. 9 is a schematic view of an embodiment of a motor vehicle includinga set of airfoils;

FIG. 10 is a schematic view of a rear portion of the motor vehicle ofFIG. 9, in which pathlines of fluid elements are indicated;

FIG. 11 is a schematic view of another embodiment of an airfoil;

FIG. 12 is a schematic view of an embodiment of a set of airfoilsassociated with a trailer;

FIG. 13 is a schematic view of the set of airfoils in FIG. 12 attachedto the trailer;

FIG. 14 is a schematic view of a set of airfoils attached to a trailer,in which the direction of airflow around one of the airfoils isindicated schematically, according to an embodiment;

FIG. 15 is a schematic view of an airfoil system and an associatedtrailer, according to an embodiment;

FIG. 16 is a schematic view of an airfoil secured to the trailer using amounting component, according to an embodiment;

FIG. 17 is a schematic view of another embodiment of an airfoil;

FIG. 18 is a schematic cross-sectional view of an embodiment of anairfoil;

FIG. 19 is a schematic view of an embodiment of a drone with multipleblades;

FIG. 20 is a schematic isometric view of a blade for a drone;

FIG. 21 is a schematic isometric view of the blade of FIG. 12;

FIG. 22 is a schematic view of multiple fluid devices that mayincorporate airfoils, according to an embodiment;

FIG. 23 is a schematic view of a set of turbine rotors with blades thatmay be associated with a turbine engine, according to an embodiment; and

FIG. 24 is a schematic view of various machines that may incorporate anairfoil, according to an embodiment.

DETAILED DESCRIPTION

The embodiments disclose various airfoils and machines that useairfoils. As used herein, the term airfoil (or aerofoil) is anystructure with curved surfaces that produces an aerodynamic force whenmoved through a fluid. As used herein, the term “fluid” may refer to anyNewtonian Fluid. In other embodiments, airfoils could be used withNon-Newtonian Fluids. As used herein, wings, blades (e.g., propellerblades, rotor blades, turbine blades), and sails comprise various kindsof airfoils.

An airfoil may include an upper or suction surface against which fluidflows at a relatively high velocity with low static pressure. An airfoilmay also include a lower or pressure surface that has a high staticpressure relative to the suction surface. Alternatively, the suction andpressure surfaces could be referred to as suction and pressure sides.The airfoil also includes a leading edge defined as the point at thefront of the airfoil with maximum curvature. The airfoil also includes atrailing edge defined as the point at the rear of the airfoil withminimum curvature. In addition, a chord line of the airfoil refers to astraight line between the leading and trailing edges. Also, a meancamber line is the locus of points midway between the upper and lowersurfaces and may or may not correspond with the chord line depending onthe shape of the airfoil.

As used herein, an airfoil has a chord length defined as the length ofthe airfoil's chord line. In addition, the airfoil has a thicknessdefined as the distance between the upper and lower surfaces along aline perpendicular to the mean camber line. The width of an airfoil istaken in a direction perpendicular to both the chord line and thethickness.

Throughout the detailed description and claims the term “radius ofcurvature” is used. The radius of curvature is the reciprocal of thecurvature at a particular location on a curve or two-dimensionalsurface. For a curve, the radius of curvature equals the radius of thecircular arc that best approximates the curve at that point. Inparticular, it should be noted that the larger the radius of curvatureof curve, the smaller the curvature (and vice versa).

FIGS. 1-2 illustrate schematic isometric views of airfoil (or blade)100, while FIG. 3 illustrates a schematic side view of airfoil 100.Referring to FIGS. 1-3, airfoil 100 is comprised of pressure side 102(shown in FIG. 1) and opposing suction side 104 (shown in FIG. 2). Eachof these sides includes a surface (e.g., a pressure surface or a suctionsurface) in contact with air during operation. Additionally, airfoil 100includes leading edge 110 and trailing edge 112. Moreover, leading edge110 and trailing edge 112 are connected by chord line 114 (see FIG. 3).

Referring to FIG. 3, in some embodiments, airfoil 100 may be comprisedof a single body 101 of material. Starting from trailing edge 112, body101 includes base portion 180 that is seen to curve gradually throughthe length of airfoil 100. Base portion 180 includes first surface 187on pressure side 102 of airfoil 100 and opposing second surface 188 onopposing suction side 104.

At the end of base portion 180, body 101 bends to create a folded orhook-like section adjacent leading edge 110. That is, adjacent leadingedge 110, body 101 is comprised of elliptic portion 142 as well asoverhang portion 182 that hands or extends over some of base portion180. Elliptic portion 142 connects base portion 180 and overhang portion182 and also includes leading edge 110.

In some embodiments, overhang portion 182 may be spaced apart orseparated from base portion 180. In the embodiment of FIG. 3, overhangportion 182 is separated from base portion 180 by gap 195. In differentembodiments, the size of gap 195 may vary. In some cases, gap 195 may begreater than or equal to a thickness of overhang portion 182. In somecases, gap 195 may be at least three times as large as a thickness ofoverhang portion 182. Ensuring that gap 195 is sufficiently large and sothat overhang portion 182 is sufficiently spaced apart from base portion180 is important to facilitate desirable airflow behavior across airfoil100 as discussed in further detail below.

The fold in body 101 adjacent leading edge 110 may be seen to divideairfoil 100 into two portions having distinctive geometries: leadingairfoil portion 120 and trailing airfoil portion 122. Leading airfoilportion 120 is seen to comprise the leading segment of base portion 180,elliptic portion 142 and overhang portion 182. In contrast, trailingairfoil portion 122 comprises only the trailing segment of base portion180.

In different embodiments, the length of leading airfoil portion relativeto the overall length of the airfoil (that is, the percent of the totalairfoil length that the overhang portion extends over) can vary. In somecases, the leading airfoil portion has a relative length of 25 to 50percent of the total airfoil length. In one embodiment, the leadingairfoil portion has a length of at least 25 percent of the total airfoillength. In yet another embodiment, the leading airfoil portion has alength of at least one third of the total airfoil length. In some cases,the leading airfoil portion may made sufficiently long enough (at least25 percent or so of the total airfoil length) so that the first arcportion can be gradually curved down towards the second arc portion,thereby helping to keep the boundary layer attached to airfoil beforethe dramatic step down in thickness adjacent the second arc portion.

As seen in FIG. 3, body 101 has a relatively constant local thickness103 throughout airfoil 100. However, the folded shape of body 101 thatforms overhang portion 182 provides a greater overall thickness throughleading airfoil portion 120 than in trailing airfoil portion 122. Here,the overall thickness is measured between opposing suction side 104 andpressure side 102 and is distinct from the local body thickness.Specifically, leading airfoil portion 120 has variable thickness 130with a maximum value adjacent leading edge 110 and a minimum value at alocation furthest from leading edge 110. In contrast, trailing airfoilportion 122 has an approximately constant thickness. In someembodiments, the thickness of trailing airfoil portion 122 isapproximately equal to local thickness 103 of body 101. In otherembodiments, trailing airfoil portion 122 could also have a variablethickness.

An airfoil may include provisions for keeping airflow “stuck” on thesuction surface so that the air can be redirected through a large angle(e.g., from a near horizontal direction for incoming air to a nearvertical direction for outgoing air). In some embodiments, an airfoilcan include a leading airfoil portion that includes one or more of arcsfor controlling the flow of air along a suction surface.

In some embodiments, overhang portion 182 may be further comprised offirst arc portion 152 and second arc portion 154. First arc portion 152may extend from elliptic portion 142, while second arc portion 154 maybe disposed at an open or free end of overhang portion 182. In someembodiments, the curvature (along opposing suction side 104) of overhangportion 182 may vary from first arc portion 152 to second arc portion154. In some cases, first arc portion 152 may be configured to curvedown in the direction of base portion 180. Moreover, second arc portion154 may be configured with steeper curvature that is also directeddownwardly toward base portion 180.

In the following description the radius of curvature of various surfacesis defined relative to the length of a unit radius, denoted as “UN”. Indifferent embodiments, the particular value of the length of the unitradius could vary. For example, the unit radius could have a length of100 mm (i.e., 1 UN=100 mm), 6 inches (i.e., 1 UN=6 inches), or any othervalue. It may be understood that the ratio of two radii of curvature isindependent of the particular value of the unit radius. Thus, if a firstsurface has a radius of curvature of 1 UN and a second surface has aradius of curvature of 0.5 UN, the ratio is equal to 1 divided by 0.5,or 2, and is a dimensionless quantity that is independent of theparticular length of the unit radius in a given embodiment.

FIG. 4 is a schematic side view of airfoil 100. Referring to FIG. 4, thedifferent portions or segments of airfoil 100 can have different degreesof curvature. In some embodiments, trailing airfoil portion 122 hastrailing arc portion 160 immediately adjacent trailing edge 112.Trailing arc portion 160 has radius of curvature 200. In some cases,radius of curvature 200 could have a value of approximately 0.1000 UN.In some embodiments, main segment 162 of trailing airfoil portion 122has radius of curvature 202 along pressure side 102 and radius ofcurvature 204 along opposing suction side 104. In some cases, radius ofcurvature 202 has a value of approximately 1.1250 UN. In some cases,radius of curvature 204 has a value of approximately 1.1750 UN. In someembodiments, elliptic portion 142 has radius of curvature 206 on outwardfacing side 170 and radius of curvature 208 on inward facing side 172.In some cases, radius of curvature 206 has a value of approximately0.1500 UN. In some cases, radius of curvature 208 has a value ofapproximately 0.1000 UN.

In some embodiments, first arc portion 152 has radius of curvature 210along opposing suction side 104 and radius of curvature 212 along inwardfacing surface 190. In some cases, radius of curvature 210 has a valueof approximately 0.7500 UN. In some cases, radius of curvature 212 has avalue of approximately 0.7000 UN. In addition, second arc portion 154has radius of curvature 214. In some cases, radius of curvature 214 hasa value of approximately 0.1000 UN.

In some embodiments, the curvature of each segment of airfoil 100 may beselected to help keep the boundary layer of flowing air attached toopposing suction side 104, even as airfoil 100 curves from leading edge110 to trailing edge 112.

FIG. 5 is a schematic view of airfoil 100 in operation as air passesacross it. Referring to FIG. 5, incoming air flows in an approximatelyhorizontal direction 300 and encounters leading edge 110 first. Airmoving across opposing suction side 104 will first pass across first arcportion 152, which curves down to second arc portion 154. Air then getsdirected down into trailing airfoil portion 122. As the air flows alongtrailing airfoil portion 122, it is directed down to trailing arcportion 160 and turns downwardly as it leaves trailing edge 112.

The geometry of leading airfoil portion 120 creates step-down region 310resulting in an abrupt change in thickness between leading airfoilportion 120 and trailing airfoil portion 122. This sudden change inthickness (and geometry) creates vortex 320 (and/or turbulent eddies) atstep-down region 310. As air flows over opposing suction side 104,vortex 320 “pulls” the air down and thereby reattaches the boundarylayer of the flow as it moves from one section to the next, keeping theair “stuck” on opposing suction side 104.

The embodiments utilize specifically curved arc portions adjacentstep-down region 310 to help actively control the turbulent eddies orvortices that develop at step-down region 310. Specifically, first arcportion 152 and second arc portion 154 combine to actively redirect thefluid flow with use of the Coand{hacek over (a)} effect towardreattachment to the airfoil upper surface. The Coand{hacek over (a)}effect refers to the tendency of a jet of fluid emerging from an orificeto follow an adjacent flat or curved surface and to entrain fluid fromthe surroundings so that a region of lower pressure develops. Vortex 320(and/or turbulent eddies) at step-down region 310 creates a pressuredifference between second arc portion 154 and trailing airfoil portion122. The active fluid flowing across opposing suction side 104 createsair curtain 322 (via the Coand{hacek over (a)} effect) that helps holdvortex 320 in place and keeps it attached to opposing suction side 104.Air curtain 322 thus provides a stabilizing force to keep vortex 320 inplace, which further serves to prevent the boundary layer fromdelaminating from airfoil 100.

This arrangement provides an airfoil that keeps the airflow stuck toopposing suction side 104 enough to turn the airflow direction by closeto 90 degrees. That is, air initially flowing in horizontal direction300 as it encounters leading edge 110 leaves trailing edge 112 travelingin second direction 302. In some cases, second direction 302 is a nearvertical direction. In other embodiments, depending on the shape andlocal curvature of various segments of airfoil 100, the direction ofincoming air could be changed by any amount between approximately 10 and90 degrees.

FIG. 6 illustrates a schematic isometric view of another embodiment ofairfoil (or blade) 500. In contrast to the open-ended or foldedconfiguration of airfoil 100, airfoil 500 has a solid geometry.Referring to FIG. 6, airfoil 500 is comprised of opposing pressure side502 and suction side 504. Additionally, airfoil 500 includes leadingedge 510 and trailing edge 512.

Airfoil 500 may be further characterized as comprising leading airfoilportion 520 and trailing airfoil portion 522. Starting from trailingedge 512, airfoil 500 is seen to curve gradually through trailingairfoil portion 522.

An airfoil may include provisions for keeping airflow “stuck” on thesuction surface and allowing air to be redirected through a large angle.In some embodiments, an airfoil can include a leading airfoil portionthat includes a series of arcs for controlling the flow of air along asuction surface.

As seen in FIG. 6, leading airfoil portion 520 is comprised of pressureside surface 540, first elliptic surface 542, suction side surface 544,and second elliptic surface 545. Pressure side surface 540 extends fromtrailing airfoil portion 522 to first elliptic surface 542. Firstelliptic surface 542 extends around from opposing pressure side 502 tosuction side 504 and includes leading edge 510. Suction side surface 544curves down toward pressure side surface 540. Second elliptic surface545 then curves down in a convex manner and connects with trailingairfoil portion 522. In contrast to the open region created by the foldin airfoil 100, the design shown in FIG. 6 provides step-down region 710with a solid, continuous and convex surface. Moreover, as in theprevious embodiment, the overall thickness 630 of leading airfoilportion 520 is greater than thickness 632 of trailing airfoil portion522.

FIG. 7 is a schematic side view of airfoil 500. Referring to FIG. 7, thedifferent portions or segments of airfoil 500 can have different degreesof curvature. In some embodiments, trailing airfoil portion 522 has arcportion 560 immediately adjacent trailing edge 512. Arc portion 560 hasradius of curvature 600. In some cases, radius of curvature 600 couldhave a value of approximately 0.1000 UN. In some embodiments, mainsegment 562 of trailing airfoil portion 522 has radius of curvature 602along opposing pressure side 502 and radius of curvature 604 alongsuction side 504. In some cases, radius of curvature 602 has a value ofapproximately 1.1250 UN. In some cases, radius of curvature 604 has avalue of approximately 1.1750 UN. In some embodiments, first ellipticsurface 542 has radius of curvature 606. In some cases, radius ofcurvature 606 has a value of approximately 0.1500 UN.

In some embodiments, suction side surface 544 has radius of curvature610. In some cases, radius of curvature 610 has a value of approximately0.7500 UN. In addition, second elliptic surface 545 has radius ofcurvature 614. In some cases, radius of curvature 614 has a value ofapproximately 0.1000 UN.

In some embodiments, the curvature of each segment of airfoil 500 may beselected to help keep the boundary layer of flowing air attached tosuction side 504, even as airfoil 500 curves from leading edge 510 totrailing edge 512.

FIG. 8 is a schematic view of airfoil 500 in operation as air passesacross it. Referring to FIG. 8, incoming air flows in an approximatelyhorizontal direction 700 and encounters leading edge 510 first. Airmoving across suction side 504 will first pass across suction sidesurface 544, which curves down to second elliptic surface 545. Air thengets directed down into trailing airfoil portion 522. As the air flowsalong trailing airfoil portion 522, it is directed down to arc portion560 and turns downwardly as it leaves trailing edge 512.

The geometry of leading airfoil portion 520 creates step-down region710, resulting in an abrupt change in thickness between leading airfoilportion 520 and trailing airfoil portion 522. This sudden change inthickness (and geometry) creates vortex 720 (and/or turbulent eddies) atstep-down region 710. As air flows over suction side 504, vortex 720“pulls” the air down and thereby reattaches the boundary layer of theflow as it moves from one section to the next, keeping the air “stuck”on suction side 504.

The embodiments utilize specifically curved arc and/or elliptic surfacesadjacent step-down region 710 to help actively control the turbulenteddies or vortices that develop at step-down region 710. Specifically,suction side surface 544 and second elliptic surface 545 combine toactively redirect the fluid flow with use of the Coand{hacek over (a)}effect toward reattachment to the airfoil upper surface. Vortex 720(and/or turbulent eddies) at step-down region 710 creates a pressuredifference between elliptic surface 545 and trailing airfoil portion522. The active fluid flowing across suction side 504 creates aircurtain 722 (via the Coand{hacek over (a)} effect) that helps holdvortex 720 in place and keeps it attached to suction side 504. Aircurtain 722 thus provides a stabilizing force to keep vortex 720 inplace, which further serves to prevent the boundary layer fromdelaminating from airfoil 500.

As with the embodiment of airfoil 100, this arrangement provides anairfoil that keeps the airflow stuck to suction side 504 enough to turnthe airflow direction by close to 90 degrees. That is, airflow initiallyflowing in horizontal direction 700 as it encounters leading edge 510leaves trailing edge 512 traveling in second direction 702. In somecases, second direction 702 is a near vertical direction. In otherembodiments, depending on the shape and local curvature of varioussegments of airfoil 500, the direction of incoming air could be changedby any amount between approximately 10 and 90 degrees.

The embodiments of airfoils discussed above, including airfoil 100 andairfoil 500 may be used in a variety of different applications. In someembodiments, airfoils may be used to direct airflow around edges of amotor vehicle, such as the rear edges. The disclosed airfoils could beused with a variety of different kinds of motor vehicles, includingtractor trailers, truck cabs, and other trucks as well as SUV's, sedans,coupes, and other cars. It may be appreciated that airfoils could alsobe used with any other kind of motor vehicle such as motorcycles, ATVs,and snowmobiles.

The following shows exemplary machines and devices utilizing an airfoilwith a folded end similar to airfoil 100. However, it may be understoodthat in other embodiments airfoils with a solid end similar to airfoil500 could also be integrated into any of these same machines anddevices.

In one exemplary application, depicted in FIG. 9, set of airfoils 808may be used to direct airflow around the back of motor vehicle 800. Inthe exemplary embodiment, motor vehicle 800 is a tractor trailer withtrailer 802. The rear end of trailer 802 includes first airfoil 810,second airfoil 812, and third airfoil 814 that are arranged along driverside rearward edge 820, top rearward edge 822, and passenger siderearward edge 824 of trailer 802, respectively. In other embodiments,airfoils could be used along only one edge, only two edges, and/or alongfour edges. In some cases, for example, an airfoil could be positionedalong lower rearward edge 826 of trailer 802.

In contrast to the design of airfoil 100 and airfoil 500, the airfoilsin set of airfoils 808 may be elongated such that a single airfoilextends the full length of each edge. Depending on the dimensions ofmotor vehicle 800, the width of the airfoil could range between 2 to 10feet. In still other cases, the airfoils could be located along someportions of an edge but not others. In such cases, airfoils could have awidth of substantially less than 2 feet. In still other applications forlarger trucks or machines, an airfoil could have a width of greater than10 feet.

In different embodiments, any means for attaching an airfoil to the edgeof a motor vehicle could be used. In some embodiments, fasteners,adhesives, welds, or other means can be used to secure an airfoil to avehicle. In other embodiments, an airfoil could be attached usingtool-less means, such as magnets or double-sided tape.

In one embodiment, an airfoil system for a motor vehicle uses a seriesof mounts 850 to attach set of airfoils 808 to motor vehicle 800. Themounts may be configured to retain the airfoil without fasteners orother direct connections, instead relying on a locking “fit” between themount and airfoil. While the present embodiment depicts approximately4-6 mounts per edge to secure a single airfoil, in other embodiments thenumber and spacing of mounts could be varied.

For example, FIG. 9 includes an enlarged isolated view of one mount 852that helps retain second airfoil 812. Mount 852 includes based portion854 that can be fastened directly to motor vehicle 800. Mount 852 alsoincludes retaining portion 856 that is shaped to receive leading airfoilportion 813 of second airfoil 812.

In some embodiments, retaining portion 856 has a hook-like geometry thatallows leading airfoil portion 813 to slide into place along mountingdirection 860 while restricting leading airfoil portion 813 from slidingout along perpendicular direction 862. In some embodiments, the ends orother portions of an airfoil could be fixed into place to prevent theairfoil from sliding along mounting direction 860 during operation ofmotor vehicle 800.

For clarity, second mount 832 is shown in isolation in FIG. 9, andincludes a similar base portion 834 and retaining portion 836 so thatthe geometry of the mount can be more clearly seen.

In operation, the use of airfoils along one or more edges allows air tofill in the void created by the moving trailer, thereby reducing drag.As seen in FIG. 10, air flowing horizontally across top surface 890 andside surfaces 892 of trailer 802 may be turned around each of edge 820,edge 822, and edge 824 by corresponding airfoils. In some cases, the airturns through an angle of near 90 degrees so that it flows nearlyparallel with rearward side 805 of trailer 802. The air then collectsimmediately behind motor vehicle 800 where a void would otherwise form.

FIGS. 11-14 illustrate schematic views of another embodiment of airfoilsthat may be attached to a truck, or other vehicle, to help direct airaround the back of the truck and reduce drag. In FIG. 11, a firstairfoil 1100 (or simply, “airfoil 1100”) is depicted in isolation. Forclarity, an enlarged cross-sectional view of airfoil 1100 is also shownin FIG. 11.

Airfoil 1100 may comprise a base portion 1102 and an extended portion1104 that extends from base portion 1102. Base portion 1102 may comprisea first surface 1106 and a second surface 1108, which both extend from alower periphery 1110 of base portion 1102 up towards extended portion1104. More specifically, both first surface 1106 and second surface 1108slope upwardly and inwardly from their respective edges along lowerperiphery 1110, with each surface extending continuously with extendedportion 1104. Additionally, a third surface 1120 and an opposing fourthsurface 1122 also extend upwardly from lower periphery 1110 to extendedportion 1104. Third surface 1120 and fourth surface 1122 each comprisethree edges giving them an approximately triangular geometry.Optionally, in some embodiments, third surface 1120 and fourth surface1122 may be absent, for example in an embodiment where airfoil 1100 hasa hollow interior. Such an embodiment is depicted, for example, in FIGS.15 and 16 and discussed in further detail below.

In some embodiments, base portion 1102 may further comprise a lowersurface 1109 that joins one or more of first surface 1106, secondsurface 1108, third surface 1120 and fourth surface 1122 along lowerperiphery 1110. However, in embodiments where base portion 1102 may havea fully, or partially, hollow interior, a lower surface may be optional.

In some embodiments, the geometry of base portion 1102 may beapproximately similar to a triangular prism, with first surface 1106,second surface 1108 and lower surface 1109 each comprising faces of aprism with four edges and with third surface 1120 and fourth surface1122 comprising faces of the prism with three edges. Moreover, extendedportion 1104 may be seen to extend along one of the edges of the prismthat connects the opposing triangular surfaces (i.e., third surface 1120and fourth surface 1122). Of course, it may be appreciated that thegeometry of base portion 1102 may vary from that of a prism, with somesurfaces (or faces) being curved rather than planar, for example.

Airfoil 1100 may have a geometry that is similar in some respects toairfoil 100. For example, as best seen in the cross-sectional view ofFIG. 11, the profile of second surface 1108 and its continuation withextended portion 1104 may have a substantially similar profile to thatof airfoil 100, as depicted, for example, in FIGS. 3-5.

As best seen in the cross-sectional view of FIG. 11, extended portion1104 has a geometry similar to portions of airfoil 100. Specifically,extended portion 1104 may comprise an elliptic portion 1130 and anoverhang portion 1132, similar in geometry to those same components inairfoil 100 (i.e., elliptic portion 142 and overhang portion 182).Overhang portion 1132 may be disposed over (i.e., face) a portion ofsecond surface 1108. Overhang portion 1132 may also curve towards secondsurface 1108.

It may be appreciated that in some embodiments, the respectivecurvatures of the inner and outer surfaces of elliptic portion 1130 andoverhang portion 1132 could be similar to the respective curvatures ofelliptic portion 142 and overhang portion 182. Specifically, overhangportion 1132 may further include a first arc portion and a second arcportion with different curvatures that help prevent the boundary layerof airflow from delaminating from airfoil 1100 as air passes acrossextended portion 1104 and is directed towards second surface 1108.

First surface 1106 is sloped up towards extended portion 1104 along afirst side of airfoil 1100, while second surface 1108 is sloped uptowards extended portion 1104 along a second side of airfoil 1100. Inuse, air may flow up first surface 1106, around extended portion 1104and back down second surface 1108, as discussed in further detail below.The geometry of each surface may be selected to best facilitate turningthe direction of airflow that passes across the airfoil (i.e., from anear horizontal direction to a near vertical direction). In oneembodiment, first surface 1106 has an approximately flat geometry with aconstant slope that acts to direct horizontally moving air up towardsextended portion 1104 of airfoil 1100. Also, second surface 1108 has acurved geometry that is similar to the curved geometry of suction side104 of airfoil 100 to help change the direction of airflow.

In some embodiments, second surface 1108 curves down below the loweredges of the other remaining surfaces of base portion 1102 (e.g., belowa lower edge 1107 of first surface 1106). This creates a turned downportion 1125 of airfoil 1100, including a lower elliptic portion 1127and a lower side surface 1129 that extends from lower elliptic portion1127 up to a position at a similar horizontal level to lower edge 1107.In use, this turned down portion may be arranged to extend out and overa rearward edge on a trailer.

FIGS. 12 and 13 are schematic isometric views of a set of airfoils and arearward portion of a trailer 1150 for a truck or other vehicle.Specifically, FIG. 12 depicts a set of airfoils prior to attachment totrailer 1150, while FIG. 13 depicts a configuration where the entire setof airfoils have been attached.

Referring to FIGS. 12-13, the set of airfoils includes first airfoil1100, second airfoil 1162 and third airfoil 1164. Each airfoil may beassociated with a specific rearward edge of trailer 1150. In theexemplary embodiment, first airfoil 1100, second airfoil 1162, and thirdairfoil 1164 are arranged along top rearward edge 1172, driver siderearward edge 1170, and passenger side rearward edge 1174 of trailer1150, respectively. In other embodiments, airfoils could be used alongonly one edge, only two edges, and/or along four edges. In some cases,for example, an airfoil could be positioned along lower rearward edge1176 of trailer 1150.

As seen in FIGS. 12-13, in some embodiments, second airfoil 1162 andthird airfoil 1164 could have different geometries. In particular,second airfoil 1162 and third airfoil 1164 could have geometries similarto the geometries of airfoil 1200 which is discussed below and shown inFIGS. 14-15. Alternatively, in some embodiments, each of the airfoilscould have a substantially similar geometry.

In operation, the use of airfoils along one or more edges allows air tofill in the void created by the moving trailer, thereby reducing drag.As seen in FIG. 14, another schematic view of trailer 1150 with theattached set of airfoils 1160, air flowing horizontally across topsurface 1180 and side surfaces 1182 of trailer 1150 may be turned aroundeach of edge 1170, edge 1172, and edge 1174 by corresponding airfoils.

Considering airflow across airfoil 1100 as a specific example, airflow1190 may be directed from a near horizontal direction up along firstsurface 1106 towards extended portion 1104. At extended portion 1104,the airflow turns and is directed back down second surface 1108. In somecases, the air turns through an angle of approximately 90 degrees sothat it flows approximately parallel with rearward side 1184 of trailer1150. The air then collects behind trailer 1150 where a void wouldotherwise form.

As seen in FIG. 14, turned down portion 1125 of airfoil 1100 may extendrearwards of, and below, top rearward edge 1172 (see FIG. 12) of trailer1150. In the exemplary embodiment depicted in FIG. 14, second airfoil1162 (see FIG. 13) and third airfoil 1164 are seen to be approximatelyflush with driver side rearward edge 1170 and passenger side rearwardedge 1172, respectively. That is, these airfoils may not include turnedportions that extend past the rearward edges of trailer 1150. Instead,the lower peripheral edges of these airfoils may generally lie in thesame plane of the rear side of the trailer. In some cases, this may helpensure doors on the trailer have adequate clearance to open.

Different embodiments may use different methods for attaching airfoil1100 to trailer 1150. In the exemplary embodiment depicted in FIG. 12,an adhesive 1135 is used to bond airfoil 1164 to trailer 1150. Exemplaryadhesives that could be used include, but are not limited to: epoxy,silicone, cyanoacrylate and UV cure adhesives. The type of adhesive usedmay be selected according to the material properties of trailer 1150and/or airfoil 1100. In some cases, an adhesive may be selected thatfacilitates bonding between plastic (the airfoil) and metal (thetrailer). It may be appreciated that the adhesive could be applied alongthe lower periphery of an airfoil (e.g., lower periphery 1110 of airfoil1100), and/or along a lower surface when one is present. In otherembodiments, an airfoil could be mounted to a trailer (or other object)using various kinds of fasteners, including screws, bolts, rivets,nails, etc.

FIGS. 15 and 16 are schematic views of another embodiment of an airfoil1200, a mounting component 1280 and a trailer 1250. Airfoil 1200 maycomprise a base portion 1202 and an extended portion 1204, as well as afirst surface 1206 and a second surface 1208.

Airfoil 1200 may have a geometry that is similar in some respects toairfoil 500. For example, as best seen in the cross-sectional view ofFIG. 15, the profile of second surface 1208 and its continuation withextended portion 1204 may have a substantially similar profile to thatof airfoil 500, as depicted, for example, in FIGS. 6-8. As seen in theenlarged cross-sectional view of FIG. 15, extended portion 1204 andsecond surface 1208 together form an upper airfoil surface that has ageometry similar to the suction surface of airfoil 500. That is, theupper airfoil surface includes a suction side surface 1220 and anelliptic surface 1222 that extends continuously with second surface1208. Moreover, as with airfoil 500, the respective of curvaturessuction side surface 1220 and elliptic surface 1222 may be different tohelp prevent the boundary layer of airflow from delaminating fromairfoil 1200 as air passes across extended portion 1204 and is directedtowards second surface 1208.

FIGS. 15 and 16 also depict an alternative method of attaching anairfoil to a trailer. Referring to FIGS. 15 and 16, the presentembodiment uses a mounting component 1280 (e.g. a mounting rail) tosecure airfoil 1200 in place. Specifically, mounting component 1280 maybe secured to trailer 1250 using conventional methods such as adhesives,fasteners (e.g., screws, rivets, etc.), welds or other methods. Thenairfoil 1200 may be attached to mounting component 1280 and therebysecured to trailer 1250.

Mounting component 1280 and airfoil 1200 may have geometries adapted tofit one another. As seen in FIG. 15, airfoil 1200 includes a first lowerportion 1230 with a first peripheral ridge 1232 as well as a secondlower portion 1231 with a second peripheral ridge 1234. These peripheralridges may be oriented towards an interior 1239 of airfoil 1200 (and soaway from the trailer when the airfoil is attached to the trailer).First lower portion 1230 and second lower portion 1231 may be separatedby a gap that receives part of mounting component 1280 when airfoil 1200is attached.

Mounting component 1280 may include a central mounting portion 1282 thatis secured directly to a trailer as well as a first engagement portion1284 and a second engagement portion 1286 on opposing sides of centralmounting portion 1282. Each engaging portion may include a slotconfigured to receive a peripheral ridge. Specifically, first engagementportion 1284 includes first slot 1285 for receiving first peripheralridge 1232 and second engagement portion 1286 includes a second slot1287 for receiving second peripheral ridge 1234. These slots may beoriented so that when central mounting portion 1282 is attached to atrailer the open side of the slots face towards the trailer (and arethus oriented to receive the upwardly oriented ridges of airfoil 1200).

As seen in FIGS. 15-16, with mounting component 1280 secured to trailer1250, airfoil 1200 may be attached by sliding it over mounting component1280 in such a way that the ridges of airfoil 1200 are engaged with thecorresponding slots in mounting component 1280. Once in place, airfoil1200 could be help in place by friction and/or by additional provisionssuch as a removable fastener (a screw, bolt, etc.).

Although FIGS. 15-16 only depict a single airfoil, other embodimentscould incorporate similar airfoils along the side rearward edges of atrailer as well.

In different embodiments, materials for an airfoil used with a vehiclecould vary. In one embodiment, an airfoil could comprise a materialincluding a plastic. Exemplary plastics include, but are not limited to:polyethylene (PE), polypropylene, acetal, acrylic, nylon (polyamides),polystyrene, polyvinyl chloride (PVC), acrylonitrile butadiene styrene(ABS) and polycarbonate. In other embodiments, an airfoil could comprisea material including a metal. An airfoil could also be manufacturedusing any known processes including 3D-printing, molding and extrusionprocesses.

In different embodiments, the dimensions of an airfoil configured foruse with a trailer could vary. As an example, in some embodiments,airfoil 1100 could have a width (i.e., a dimension extending betweenfirst surface 1106 and second surface 1108) in the range ofapproximately 0.5 to 4 feet. In some embodiments, an airfoil could havea width greater than 4 feet. In one embodiment, airfoil 1100 could havea width of approximately 3½ feet. In some embodiments, airfoil 1100could have a height in the range of approximately 0.5 to 1.5 feet. Insome embodiments, an airfoil could have a height of approximately 1foot. In some embodiments, the height of an airfoil could be constrainedby factors including overhead clearance (along the top) and/or clearancewith rear doors along the sides.

It may be appreciated that while the exemplary embodiments depict aconfiguration with airfoils disposed approximately at the rearward mostedges of a trailer (i.e., the top rearward edge and opposing siderearward edges) in other embodiments airfoils could be disposed atdifferent positions with respect to a rearward edge. In some cases,portions of an airfoil could extend past a rearward edge. In othercases, an airfoil could be positioned so its spaced away from anadjacent rearward edge.

FIGS. 17 and 18 illustrate another embodiment of an airfoil 1300.Specifically, FIG. 17 illustrates a schematic isometric view of anembodiment of airfoil 1300 along with an enlarged cross-sectional view.FIG. 18 is a schematic cross-sectional view of airfoil 1300demonstrating how air may flow across various surfaces.

Referring now to FIG. 17, airfoil 1300 may include similar provisions toairfoil 1100 described above. Specifically, airfoil 1300 may include afirst surface 1310 and a second surface 1312 for directing air up andover an extended portion 1308 of airfoil 1300. Likewise, in someembodiments, airfoil 1300 includes a third surface 1314 and a fourthsurface 1316 at opposing ends.

For purposes of clarity, airfoil 1300 may be characterized as comprisingsurfaces associated with different airfoil types. As used herein, theterm “open airfoil type” refers to an airfoil or portion of an airfoilwhere the leading end has a folded, or open, geometry. An example of anopen airfoil type is airfoil 100, described above and shown, forexample, in FIGS. 1-5. As used herein, the term “closed airfoil type”refers to an airfoil or portion of an airfoil where the leading end hasa closed geometry. An example of a closed airfoil type is airfoil 500,described above and shown, for example, in FIGS. 6-8.

Airfoil 1300 may comprise two different types of airfoil surfaces thatare stacked, or otherwise adjacent one another, with some spacingbetween them. Specifically, airfoil 1300 includes a first airfoilportion 1302 and a second airfoil portion 1304 that are each associatedwith a distinct type of suction-side surface. First airfoil portion 1302includes extended portion 1308 and second surface 1312. Extended portion1308 and second side surface 1312 may have a geometry similar to airfoil1100 and to airfoil 100 (i.e., the geometry may be similar to thesuction side of airfoil 100). Second airfoil portion 1304 includes firstsurface 1310, outer suction surface 1330, elliptic surface 1332 and aninterior suction surface 1334. Together, outer suction surface 1330,elliptic surface 1332 and interior suction surface 1334 may have asimilar geometry to airfoil 1200 and airfoil 500 (i.e., the geometry maybe similar to the suction side of airfoil 500).

In some embodiments, a passageway 1370 extends through airfoil 1300 toprovide access to interior suction surface 1334. Passageway 1370 may beopen at upper opening 1338 and lower opening 1336, so that air can flowfrom the top of airfoil 1300 to the bottom.

Using two airfoil surfaces may help improve airflow by directingincoming (horizontal) air down across two separate suction surfaces andincreasing the volume of air that can be directed down. As seen in FIG.18, in operation incoming airflow 1350 travels up first surface 1310 toouter suction surface 1330. Some of this airflow 1350 takes a firstairflow path 1352 through upper opening 1338, down elliptic surface 1332and then further down along interior suction surface 1334 before exitingthrough lower airfoil opening 1336. Some of the air reaching outersuction surface 1330 may take a second airflow path 1354 that flows upto, and around, extended portion 1308, and then back down second surface1312. Moreover, in some cases, the angle of attack of the airfoilsurface associated with first airfoil portion 1302 helps capture airtraveling horizontally at a higher level above first surface 1310. Forexample, air flowing along airflow path 1356 may flow horizontally untilcatching the leading edge of extended portion 1308 and being drawn downalong second surface 1312.

In another embodiment, depicted in FIGS. 19-21, airfoils havinggeometries similar to airfoil 100 or airfoil 500 could be used as bladesin a drone. FIGS. 19-21 depict a particular blade design for quadcopterdrone 900 with four blades 901. In this exemplary design, as shown inFIGS. 20-21, blade 902 has central hub 904 for mounting to a shaft, aswell as first blade section 906 and second blade section 908. In thiscase, each blade section has a geometry similar to airfoil 100. In sucha design, the blade geometry may help improve thrust as the blades ofquadcopter drone 900 rotate. Although the embodiment depicts a drone, inother embodiments similar airfoil geometries could be used with any kindof rotary wing aircraft, such as helicopters (e.g., helicopter 1002 inFIG. 24).

The disclosed airfoil shapes can be applied to any kind of rotarykinetic fluid motor or pump in which the motor, pump, or similar deviceincludes a runner and in which a working fluid is guided to, around, orfrom, the runner. Such devices may include, but are not limited to,turbines, wheels, centrifugal pumps, and blowers. The disclosed airfoilshapes can also be applied to any kind of fluid reaction surfaces,including impellers, which are acted on, or act on, a working fluid.

As shown in FIG. 22, exemplary airfoil 957 and airfoil 959 could be usedas blades in centrifugal pump 952 and/or blades in centrifugal blower954, respectively. In some embodiments, airfoil 957 and airfoil 959 maybe configured with different dimensions according to their intended use.For example, airfoil 957 may be longer than airfoil 959. Additionally,airfoil 957 may have a smaller width than airfoil 959. This differencein geometry reflects the respective applications of each airfoil incentrifugal pump 952 and centrifugal blower 954. Though exemplaryairfoils 957 and airfoil 959 are depicted as similar to airfoil 100 inshape (i.e. each includes an overhang portion), it may be appreciatedthat the design is only exemplary and the exact dimensions, materials,and/or other properties could be varied according to the particular use(e.g., in a pump or a blower). Moreover, in some cases, one or both ofairfoil 957 and airfoil 959 could alternatively have a solid geometrylike airfoil 500.

FIG. 23 is a schematic isometric view of engine 980 that includes one ormore turbines. It may be appreciated that engine 980 is shownschematically and the specific rotors depicted herein could be deployedin a variety of different engine configurations. Referring to FIG. 23, asection of turbine rotors 982 adapted for use in engine 980 may beconfigured with blades 984. Each of blades 984 may have a geometrysimilar to that of airfoil 100. In the exemplary embodiment, first rotor991, third rotor 993, and fifth rotor 995 comprise of blades arranged ina first orientation while second rotor 992 and fourth rotor 994 compriseblades arranged in a second orientation that is different from the firstorientation. In some cases, first rotor 991, third rotor 993, and fifthrotor 995 may be configured to rotate in a first direction, while secondrotor 992 and fourth rotor 994 may be configured to rotate in a seconddirection. Although not shown in FIG. 23, some embodiments couldincorporate one or more sets of planetary gears to facilitate counterrotation of one set of rotors. Also, in some embodiments, a shroud (orrunner) could be used with one or more sets of rotors. In someembodiments, rotors 982 could be used in either a high-pressurecompressor or low-pressure turbine of engine 980. In some embodiments,one or more of rotors 982 could be used as part of an intake fan of anengine 980.

FIG. 24 depicts a variety of other machines that may use airfoils havingany of the properties discussed above including any of the features ofairfoil 100 or airfoil 500. Specifically, airfoil 1000 could beincorporated into the blades, rudders, or other control surfaces ofhelicopter 1002. Airfoil 1000 could also be incorporated into the bladesof wind turbine 1004. Airfoil 1000 could also be incorporated into theblades of fan 1006. Airfoil 1000 could also be incorporated as a fixedwing in various kinds of aircraft, including glider 1008. Airfoil 1000could also be incorporated into a car 1010, for example, to operate as aspoiler.

It may be appreciated that airfoils with the disclosed shapes can beused on any surface of a machine or device that contacts a workingfluid. In some cases, airfoils with the disclosed shapes could be usedon control surfaces of an aircraft such as ailerons, elevators, rudders,spoilers, flaps, slats, air brakes, elevator trims, rudder trims, andaileron trims. Moreover, airfoils with the disclosed shapes could beused on any rotors (e.g., main and tail rotors in a helicopter) and/orpropellers of an aircraft.

In different embodiments, airfoils could be manufactured from variousmaterials. Exemplary materials include, but are not limited to,materials known for use in manufacturing turbine blades (e.g., U-500,Rene 77, Rene N5, Rene N6, PWA1484, CMSX-4, CMSX-10, Inconel, GTD-111,EPM-102, Nominic 80a, Niminic 90, Nimonic 105, Nimonic 105 and Nimonic263). Other materials include ceramic matrix composites. Other materialsfor airfoils can include, but are not limited to, aluminum, compositematerials, steel, titanium as well as other materials.

Airfoils can be manufactured using any known methods. In someembodiments, an airfoil can be formed using an extrusion process.

The dimensions of an airfoil can vary according to its intendedapplication. The chord line length, width, and thickness can all bevaried in different ratios while maintaining the general profile shapeof airfoil 100 (i.e., an open design) or of airfoil 500 (i.e., a soliddesign). For example, blades in a turbine may generally be smaller thanairfoils used on a truck.

While various embodiments of the invention have been described, thedescription is intended to be exemplary, rather than limiting, and itwill be apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible that are within the scopeof the invention. Any element of any embodiment may be substituted foranother element of any other embodiment or added to another embodimentexcept where specifically excluded. Accordingly, the invention is not tobe restricted except in light of the attached claims and theirequivalents. Also, various modifications and changes may be made withinthe scope of the attached claims.

1. An airfoil, comprising: a leading edge and a trailing edge; a suctionside and a pressure side; a base portion including a first surfaceassociated with the pressure side and a second surface associated withthe suction side; an overhang portion that extends over some of the baseportion; an elliptic portion connecting the base portion and theoverhang portion adjacent the leading edge; and wherein the overhangportion is curved toward the second surface of the base portion.
 2. Theairfoil according to claim 1, wherein the overhang portion comprises afirst arc portion having a first radius of curvature on the suction sideand the overhang portion comprising a second arc portion having a secondradius of curvature on the suction side that is different from the firstradius of curvature.
 3. The airfoil according to claim 2, wherein thesecond radius of curvature is greater than the first radius ofcurvature.
 4. The airfoil according to claim 1, wherein a free end ofthe overhang portion is separated from the base portion by a gap, andwherein the gap is substantially greater than a local thickness of theoverhang portion.
 5. The airfoil according to claim 4, wherein the gapis at least twice as large as the local thickness of the overhangportion.
 6. The airfoil according to claim 1, wherein: the base portionis comprised of a leading end section and a trailing end section, theleading end section being disposed beneath the overhang portion; whereinthe leading end section of the base portion, the elliptic portion, andthe overhang portion collectively comprise a leading airfoil portion;and wherein the leading airfoil portion is thicker than the trailing endsection of the base portion.
 7. The airfoil according to claim 6,wherein a leading end thickness of the airfoil defined as a distancebetween the first surface of the leading end section of the base portionand the suction side of the overhang portion has a maximum valueadjacent the elliptic portion and a minimum value adjacent a free end ofthe overhang portion.
 8. The airfoil according to claim 1, wherein thebase portion has a first radius of curvature on the suction side at thetrailing edge and a second radius of curvature on the suction sideadjacent the trailing edge, and wherein the first radius of curvature issmaller than the second radius of curvature.
 9. The airfoil according toclaim 1, wherein the base portion has a first length, wherein theoverhang portion has a second length, and wherein the second length isat least ¼ of the first length.
 10. An airfoil, comprising: a leadingedge and a trailing edge; a suction side and a pressure side; a leadingairfoil portion including the leading edge and a trailing airfoilportion including the trailing edge; the leading airfoil portionincluding a pressure side surface, a first elliptic surface, a suctionside surface and a second elliptic surface; the first elliptic surfaceconnecting the pressure side surface with the suction side surface andthe second elliptic surface connecting the suction side surface with thesuction side of the trailing airfoil portion; and wherein a thickness ofthe airfoil decreases from the leading airfoil portion to the trailingairfoil portion.
 11. The airfoil according to claim 10, wherein thesuction side surface is comprised of an arc having a first radius ofcurvature, and wherein the second elliptic surface has a second radiusof curvature that is different from the first radius of curvature. 12.The airfoil according to claim 11, wherein the second radius ofcurvature is substantially less than the first radius of curvature. 13.The airfoil according to claim 10, wherein the second elliptic surfaceis a convex surface.
 14. The airfoil according to claim 10, wherein theleading airfoil portion has a variable thickness, and wherein thethickness decreases from the first elliptic surface to the secondelliptic surface.
 15. The airfoil according to claim 10, wherein thetrailing airfoil portion has an approximately constant thickness.
 16. Anairfoil for use with a motor vehicle trailer, comprising: a base portionand an extended portion extending from the base portion; the baseportion including a lower periphery, a first surface and a secondsurface, wherein the first surface extends from the lower periphery tothe extended portion and wherein the second surface extends from thelower periphery to the extended portion; and wherein the extendedportion extends over the second surface.
 17. The airfoil according toclaim 16, wherein the extended portion includes an overhang portion thatextends over some of the second surface of the base portion and whereinthe extended portion includes an elliptic portion connecting the baseportion and the overhang portion.
 18. The airfoil according to claim 16,wherein: the extended portion includes a suction side surface thatextends continuously with the first surface of the base portion andwherein the extended portion includes an elliptic surface that extendsfrom the suction side surface to the second surface of the base portionsuch that a portion of the elliptic surface faces towards the secondsurface.
 19. The airfoil system according to claim 16, wherein theairfoil includes ridges along a lower side of the base portion andwherein the ridges are configured to engage slots in a mountingcomponent on a trailer.
 20. The airfoil system according to claim 16,wherein the airfoil includes a turned down portion that extendscontinuously with the second surface, and wherein the turned downportion is configured to hang over a rearward edge of a trailer.